The present invention relates to methods to produce keratin elastomer, involving:                (A)(1) reacting a diisocyanate with a blocking agent to form a diisocyanate with one —NCO group blocked by the blocking agent and one —NCO group unblocked,        (2) reacting the diisocyanate with one —NCO group blocked by the blocking agent and one —NCO group unblocked with keratin at about 100° to about 120° C. to form keratin urethane with —NCO group functionality (i.e., with one —NCO group unblocked),        (3) optionally reacting the keratin urethane with —NCO group functionality with a compound capable of reacting with the —NCO group;        (B) reacting a diisocyanate with keratin to form keratin elastomer; or        (C) reacting a monoisocyanate with keratin to form keratin elastomer.        
Isocyanates were discovered by Wurtz in 1849 and their uses in polyurethane (PU) began in 1937. Polyurethane plastics are produced by the condensation reaction of a polyol and a diisocyanate to form carbamate, the chemical unit in elastomers. Polyurethanes are the major products in which isocyanates are used. For example, 4,4-methylene bis (isocyanatocyclohexane) was reacted with various polyols such as polyethylene glycol (PEG) to form a film coating to waterproof textiles (Tsai, H.-C., et al., Textile Research J., 77(9): 710-720 (2007)). Diisocyanates and low molecular weight diols and amines react to form polyurethane through crosslinking where the product has hard and soft domains that determine modulus, toughness, and creep resistance. Themoplastic polyurethanes exhibit high toughness and abrasion resistance, and are synthesized from three principal reactants: a difunctional polyol HO(RO)xH which determines soft segment length, a difunctional chain extender HOR′OH, which determines hard segment structure, and a diisocyanate (1+y) OCNR″NCO reacting agent. The urethane product combines hard and soft segments along the polyurethane linear molecular chain through carbamate linkages with the hard and soft segments determining mechanical properties of the product.
Diisocyanates were used to couple two proteins, bovine serum albumin (BSA) and bovine gamma globulin (BGG). Urethane-based castor oil was synthesized with free isocyanate groups to react with amino groups present in biological systems to form products for surgical adhesives used for haemostasis, sealing air leakage, and tissue adhesion in wound mediation. These bio-based adhesives were biodegradable and biocompatible (Ferreira, P., et al., Biological Macromolecules, 40: 144-152 (2007)). Reactive polyisocyanates systems were formed from PU prepolymer and microencapsulated isophorone diisocyanate healing agent as an active and responsive system for self-healing. In this system, toluene diisocyanate (TDI) was reacted with chain extender, 1,4-butanediol, to form a prepolymer for subsequent encapsulation of isophorone diisocyanate, a monomeric aliphatic diisocyanate used in abrasion and UV resistant coatings (Yang, J., et al., Macromolecules, 41: 9650-9655 (2008)). Biobased polyurethane was derived from canola oil derived polyols and diisocyanate as a substitute for petrochemical derivatives (Hojabri, L., et al., Biomacromolecules, 10: 884-891 (2009); U.S. Pat. No. 3,691,225). Biomedical polyurethane was synthesized as segmented polyether polyurethane containing hard segments of urea and soft segments of polyether linked by the urethane group for orthopedic implant applications (Wong, E. W., Development of a Biomedical Polyurethane, In: Urethane Chemistry and Applications, K. N. Edwards, Ed., ACS Symposium Series 172, Chapter 31, “Development of a Biomedical Polyurethane,” pages 489-502, 1981). Hydrogels were prepared by the reaction of chitosan with blocked diisocyanate for uses as scaffolds for tissue engineered medical products (Lin-Gibson, S., et al., Carbohydrate Polymers, 54: 193-199 (2003)).
We have produced a bio-based keratin elastomer which can be reacted with other compounds (e.g., poly(ethylene glycol)) through the amino terminus of the keratin protein in order to produce compounds which can provide high value-added keratin-based materials for cosmetic and biomedical applications.